U.S. patent application number 12/375530 was filed with the patent office on 2010-03-25 for lighting assembly.
This patent application is currently assigned to OSRAM OPTO SEMICONDUCTORS GMBH. Invention is credited to Hubert Ott, Mario Wanninger, Markus Zeiler.
Application Number | 20100073907 12/375530 |
Document ID | / |
Family ID | 38692073 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100073907 |
Kind Code |
A1 |
Wanninger; Mario ; et
al. |
March 25, 2010 |
Lighting Assembly
Abstract
A lighting arrangement comprises an optical apparatus (4) with a
radiation outlet surface (41) and an optoelectronic component (2)
for producing radiation, with an element (3) which is formed like a
reflector being formed. The shape and arrangement of the element
are suitable for deflecting radiation generated in the component
through the radiation outlet surface, and the element is designed
to specifically absorb this radiation. The lighting arrangement is
preferably intended for particularly homogeneous back-lighting of
display apparatuses such as liquid crystal displays (LCDs).
Inventors: |
Wanninger; Mario;
(Harting/Regensburg, DE) ; Zeiler; Markus;
(Nittendorf, DE) ; Ott; Hubert; (Bad Abbach,
DE) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE LLP
551 FIFTH AVENUE, SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
OSRAM OPTO SEMICONDUCTORS
GMBH
REGENSBURG
DE
|
Family ID: |
38692073 |
Appl. No.: |
12/375530 |
Filed: |
July 27, 2007 |
PCT Filed: |
July 27, 2007 |
PCT NO: |
PCT/DE07/01348 |
371 Date: |
September 9, 2009 |
Current U.S.
Class: |
362/97.1 ;
362/311.01; 362/311.02; 362/311.06 |
Current CPC
Class: |
G02B 3/04 20130101; H01L
33/60 20130101; H01L 2224/73265 20130101; H01L 2224/48247 20130101;
H01L 2224/48091 20130101; H01L 2224/48091 20130101; H01L 33/58
20130101; H01L 2224/48247 20130101; H01L 2924/00014 20130101; H01L
33/44 20130101; H01L 2224/32245 20130101; H01L 2924/00 20130101;
H01L 2224/73265 20130101; H01L 2224/32245 20130101 |
Class at
Publication: |
362/97.1 ;
362/311.01; 362/311.06; 362/311.02 |
International
Class: |
G09F 13/04 20060101
G09F013/04; F21V 5/00 20060101 F21V005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2006 |
DE |
102006035635.7 |
Claims
1. A lighting arrangement, comprising: an optical apparatus with a
radiation outlet surface: an optoelectronic component for producing
radiation: and an element shaped like a reflector having a shape
and arrangement adapted for deflecting radiation generated in the
optoelectronic component through the radiation outlet surface, and
being adapted to specifically absorb radiation which is generated
in the component.
2. The lighting arrangement according to claim 1, wherein the
radiation outlet surface has a concave-curved subarea and a
convex-curved subarea which at least partially surrounds the
concave-curved subarea.
3. The lighting arrangement according to claim 2, wherein the
optical apparatus has an optical axis, and the optical axis passes
through the concave-curved subarea of the radiation outlet
surface.
4. The lighting arrangement according to claim 3, wherein the
radiation outlet surface is rotationally symmetrical with respect
to the optical axis.
5. The lighting arrangement according to claim 1, wherein the
optical apparatus is attached to the optoelectronic component.
6. The lighting arrangement according to claim 1, wherein the
optoelectronic component comprises at least one semiconductor chip
which is suitable for radiation production.
7. The lighting arrangement according to claim 6, wherein the
semiconductor chip is formed as a thin-film semiconductor chip.
8. The lighting arrangement according to claim 7, wherein a surface
of the semiconductor chip forms a main radiation output surface,
and a side surface forms a secondary radiation outlet surface.
9. The lighting arrangement according to claim 6, wherein the
radiation outlet surface has a concave-curved subarea and a
convex-curved subarea which at least partially surrounds the
concave-curved subarea; wherein the optical apparatus has an
optical axis, and the optical axis passes through the
concave-curved subarea of the radiation outlet surface wherein the
radiation outlet surface is rotationally symmetrical with respect
to the optical axis, and wherein the optical axis passes through
the semiconductor chip.
10. The lighting arrangement according to claim 6, wherein the
minimum distance between the radiation outlet surface and the
semiconductor chip is less than or equal to 5 mm.
11. The lighting arrangement according to claim 6, wherein the
optical apparatus is adapted to form an emission characteristic
which is predetermined for the lighting arrangement, with radiation
which is output from the semiconductor chip being at least
partially prevented from striking the radiation outlet surface
after reflection within the lighting arrangement.
12. A lighting arrangement, comprising an optoelectronic component
having at least one semiconductor chip for radiation generation, is
formed as a thin-film semiconductor chip, and has a surface which
is embodied as a main radiation output surface and a side surface
which forms a secondary radiation outlet surface, with an element
shaped like a reflector having a shape and arrangement that are
suitable for deflecting at least a part of the radiation which
emerges from the secondary radiation outlet surface, and with the
element which is formed like a reflector being adapted to
specifically absorb radiation which is emitted from the
semiconductor chip.
13. The lighting arrangement according to claim 1 wherein the
element which is formed like a reflector is manufactured at least
partly from a material which absorbs radiation that is generated in
the optoelectronic component, or from an absorbent material
composition, or is provided at least partly with a material which
absorbs the radiation that is generated in the optoelectronic
component, or with an absorbent material composition.
14. The lighting arrangement according to claim 1, wherein the
element which is formed like a reflector is manufactured at least
partly from black material or from a black material composition, or
is provided at least partly with a black material or a black
material composition.
15. The lighting arrangement according to claim 1, wherein the
reflectivity of the element which is formed like a reflector and is
designed to be absorbent is less than or equal to 30%.
16. The lighting arrangement according to claim 7, wherein the
semiconductor chip comprises a carrier and a semiconductor body,
which comprises a semiconductor layer sequence with an active area
which is intended to generate radiation, with the semiconductor
body being arranged on the carrier and with the carrier being
different from a growth substrate of the semiconductor layer
sequence.
17. The lighting arrangement according to claim 16, wherein a
mirror layer is arranged between the semiconductor body and the
carrier.
18. The lighting arrangement according to claim 17, wherein the
mirror layer contains a metal or is metallic.
19. The lighting arrangement according claim 1, wherein the
optoelectronic component contains the element which is formed like
a reflector.
20. The lighting arrangement according to claim 6, wherein the
optoelectronic component comprises a housing body and an external
electrical connecting conductor, with the housing body containing
the element which is formed like a reflector, and with the
semiconductor chip being mounted on the connecting conductor.
21. The lighting arrangement according to claim 20, wherein the
element which is formed like a reflector is formed by means of a
wall of a cavity in the housing body.
22. The lighting arrangement according to claim 21, wherein the
semiconductor chip is arranged in the cavity in the housing
body.
23. The lighting arrangement according to claim 20, wherein the
housing body contains a ceramic.
24. The lighting arrangement according to claim 23, wherein the
housing body is manufactured from a black ceramic, or the housing
body is blackened.
25. The lighting arrangement according to claim 20, wherein the
housing body contains a plastic.
26. The lighting arrangement according to claim 25, wherein the
housing body is manufactured from black plastic or the housing body
is blackened.
27. The lighting arrangement according to claim 1, wherein the
lighting arrangement is adapted for back-lighting of a display
apparatus.
Description
[0001] The invention relates to a lighting arrangement having an
optoelectronic component as a radiation source.
[0002] This patent application claims the priority of German patent
application 10 2006 035 635.7, the disclosure content of which is
hereby incorporated by reference.
[0003] Lighting arrangements such as LEDs, which are intended for
back-lighting of display apparatuses, are frequently subject to the
problem that the display apparatus is not illuminated sufficiently
homogeneously. For example, subareas which are illuminated
particularly strongly can have a disturbing effect when viewing the
display apparatus.
[0004] An object of the present invention is to specify a lighting
arrangement whose emitted radiation is shaped or can be shaped in a
simplified manner and reliably, according to a predetermined
emission characteristic. According to the invention, this object is
achieved by a lighting arrangement according to one of the
independent patent claims. Advantageous refinements and
developments of the invention are the subject matter of the
dependent patent claims.
[0005] In a first embodiment, a lighting arrangement according to
the invention comprises an optical apparatus with a radiation
outlet surface and an optoelectronic component for producing
radiation, with an element which is formed like a reflector being
formed, whose shape and arrangement are suitable for deflecting
radiation generated in the component through the radiation outlet
surface, and with the element being designed to specifically absorb
radiation which is generated in the component.
[0006] During operation of the lighting arrangement, the radiation
which emerges through the radiation outlet surface is predominantly
that which is generated in the optoelectronic component and strikes
the optical apparatus without previously being reflected in the
lighting arrangement, in particular on the element which is formed
like a reflector. Radiation which would emerge through the
radiation outlet surface after reflection on the element which is
formed like a reflector is in contrast predominantly absorbed,
since the element which is formed like a reflector is designed to
specifically absorb the radiation which is generated in the
optoelectronic component. It is therefore advantageously possible
to reduce the radiation component which emerges from the radiation
outlet surface after being reflected one or more times in the
lighting arrangement, and thus emerges at an angle which can be
controlled only with difficulty. The total radiation emerging from
the radiation outlet surface can therefore be shaped in a
simplified manner according to a predetermined emission
characteristic.
[0007] The optical apparatus is preferably a separate component
from the optoelectronic component.
[0008] In a preferred refinement, the optoelectronic component
contains at least one semiconductor chip which is suitable for
radiation generation. The semiconductor chip has a surface which
faces the optical apparatus, and a side surface. Radiation which is
generated in the semiconductor chip can emerge through these
surfaces.
[0009] The element which is formed like a reflector is preferably
designed and arranged relative to the semiconductor chip such that
the majority of the radiation which emerges from the side surface
of the semiconductor chip strikes the element which is formed like
a reflector, and is specifically absorbed by it. This avoids
radiation which is output from the semiconductor chip striking the
radiation outlet surface not directly but only after being
reflected one or more times within the lighting arrangement. The
optical apparatus is therefore provided primarily with radiation
which emerges through the surface of the semiconductor chip. This
radiation which emerges from the surface is not reflected before
striking the radiation outlet surface and can be shaped by the
optical apparatus in a simplified manner, according to a
predetermined emission characteristic.
[0010] The total radiation power which emerges from the radiation
outlet surface of the optical apparatus is reduced by the
proportion of the radiation power which is generated by the
optoelectronic component and is absorbed by the element which is
formed like a reflector and is designed to be specifically
absorbent. This relates in particular to the radiation emerging
from the side surface of the semiconductor chip. However, if it
were not absorbed, but were passed to the optical apparatus, this
radiation component could be shaped by said optical apparatus only
with difficulty according to the predetermined emission
characteristic. This is particularly true if the optical apparatus
is designed and is arranged to be suitable for beamshaping of the
radiation which emerges from the surface, which generally has a
small area. For an optical apparatus such as this, radiation which
strikes after reflection has an undesirable scattered radiation
component. This scattered radiation component can be reduced by the
specifically absorbent form of the element which is formed like a
reflector. The radiation which emerges from the lighting
arrangement and is preferably in the visible spectral range can in
consequence be shaped in a simplified manner according to an
emission characteristic which is predetermined for the lighting
arrangement, and in particular is directional.
[0011] According to a further preferred refinement, the
semiconductor chip is a thin-film semiconductor chip, with that
surface of the semiconductor chip which faces the optical apparatus
being embodied as a main radiation output surface, and with the
side surface forming a secondary radiation outlet surface. The
radiation power which emerges from the main radiation output
surface is in this case greater than the radiation power which
emerges from the secondary radiation outlet surface. The sum of the
radiation power which emerges from the secondary radiation outlet
surfaces is preferably less than the radiation power which emerges
through the main radiation output surface.
[0012] In a further embodiment, a lighting arrangement according to
the invention comprises an optoelectronic component having at least
one semiconductor chip which is intended for radiation production,
is a formed as a thin-film semiconductor chip, and has a surface
which is embodied as a main radiation output surface and a side
surface which forms a secondary radiation outlet surface, with an
element which is formed like a reflector being formed, whose shape
and arrangement are suitable for deflecting at least a part of the
radiation which emerges from the secondary radiation outlet
surface, and with the element being designed to specifically absorb
radiation which is emitted from the semiconductor chip.
[0013] A lighting arrangement designed in this way provides
radiation which is generated by the thin-film semiconductor chip
and the majority of which emerges from the main radiation output
surface. The majority of the radiation which emerges from the side
surfaces is in contrast predominantly absorbed by the element which
is formed like a reflector and is designed to be specifically
absorbent. The radiation which strikes a separate downstream optics
is thus emitted from a precisely defined surface, the main
radiation output surface of the thin-film semiconductor chip, and
can be shaped in a simplified manner according to a predetermined
emission characteristic.
[0014] In a preferred refinement, the lighting arrangement
comprises an optical apparatus having a radiation outlet surface
through which radiation which is generated by the thin-film
semiconductor chip can emerge from the lighting arrangement.
[0015] A thin-film semiconductor chip comprises a carrier and a
semiconductor body with a semiconductor layer sequence, with the
semiconductor body being arranged on the carrier. In contrast to a
conventional semiconductor chip, in the case of a thin-film
semiconductor chip, the carrier is different from a growth
substrate on which the semiconductor layer sequence is deposited,
for example by means of epitaxy. The growth substrate can be
removed or thinned in places or completely. By way of example, this
can be done mechanically or chemically. The carrier is used to make
the semiconductor body mechanically robust. The growth substrate is
no longer required for this purpose.
[0016] In contrast to the growth substrate, the carrier
advantageously need not comply with the stringent requirements for
crystalline purity but can, in fact, be selected on the basis of
other criteria, such as mechanical robustness, optical, thermal or
electrical characteristics.
[0017] In a preferred refinement, a mirror layer is arranged on the
semiconductor body. The mirror layer is preferably arranged between
the carrier and the semiconductor body. Furthermore, the mirror
layer preferably contains a metal or a metallic alloy, or is
designed to be metallic. By way of example, the mirror layer may
contain Au, Al, Ag, Pd, Rh or Pt or an alloy with at least one of
these materials. For example, Au is distinguished by high
reflectivity in the red or infrared spectral range, while Ag or Al
exhibits high reflectivity in the blue or ultraviolet spectral
range, as well.
[0018] Radiation which is generated in the active area and runs in
the direction of the carrier can be reflected on the mirror layer
and can be emitted on a surface of the semiconductor chip which
faces away from the carrier and forms the main radiation output
surface, thus advantageously increasing the radiation component
which is emitted through the main radiation output surface.
Furthermore, the mirror layer can prevent radiation from being
absorbed by the carrier material, thus further increasing the
degrees of freedom for choice of the carrier material.
[0019] In thin-film semiconductor chips, the radiation power which
emerges from the side secondary radiation outlet surfaces is
decreased in favour of more radiation power being output from the
main radiation output surface. Since the lighting arrangement
preferably essentially provides only the radiation which emerges
from the surface of the semiconductor chip, while the radiation
which emerges from the side surface is predominantly absorbed by
the element which is formed like a reflector and is designed to be
specifically absorbent, the use of a thin-film semiconductor chip
as a radiation source advantageously increases the radiation power
which is emitted from the lighting arrangement. Thin-film
semiconductor chips are therefore particularly suitable for use as
a radiation source.
[0020] The element which is formed like a reflector may be
considered to be an element in the lighting arrangement or an
element which is integrated in the optoelectronic component, whose
shape and arrangement relative to the optoelectronic component, in
particular if appropriative relative to its semiconductor chip,
and/or relative to the optical apparatus, is suitable for
deflection of radiation which is emitted from the optoelectronic
component and strikes the element, at least partially, directly or
indirectly through the radiation outlet surface. The shape of the
element which is formed like a reflector can be chosen freely
within wide limits provided that, on the basis of its shape and
arrangement, at least a part of the radiation which is generated in
the optoelectronic component could be deflected by this element
through the radiation outlet surface, and in particular would be
deflected to a greater extent if the specifically absorbing design
were dispensed with. For example, the element which is formed like
a reflector may be in the form of a flat or a curved surface.
[0021] The element which is formed like a reflector is regarded as
being specifically absorbent if the reflectivity of the element
which is formed like a reflector is 49% or less, in particular 30%
or less, preferably 15% or less, and particularly preferably 5% or
less, for radiation which is generated in the optoelectronic
component. A value which is low as possible for the reflectivity of
the element which is formed like a reflector is advantageous since
this reduces the component of radiation which is reflected on the
element which is formed like a reflector. In fact, the radiation is
absorbed to a corresponding extent. The element which is formed
like a reflector and is designed to be absorbent is typically
designed such that radiation which is generated by the
optoelectronic component is not transmitted through this element.
The absorption degree A of the element which is formed like a
reflector and is designed to be specifically absorbent, and the
reflectivity R, which is also referred to as the reflection degree,
are therefore linked to one another by the relationship A=1-R.
[0022] An element which is obviously in the form of a reflector
with residual absorption which cannot be avoided or can be avoided
only with great effort should not be regarded as being designed to
be specifically absorbent, in the above sense. This relates not
only to directionally reflective elements, in general such as
metallic elements or elements with a metal surface, but also to
diffusively reflective elements, such as white plastic mouldings,
which are typically used for a housing body for optoelectronic
components, such as light-emitting diodes.
[0023] In a preferred refinement, the element which is formed like
a reflector is manufactured entirely or at least in places from a
material which absorbs radiation that is generated in the
optoelectronic component, or from an absorbent material
composition, or is provided entirely or in places with a material
which absorbs the radiation that is generated in the optoelectronic
component, or with an absorbent material composition, for example
by being coated, printed or stamped.
[0024] In a particularly preferred refinement, the element which is
formed like a reflector is manufactured completely or partially
from black, dark-grey or blackened material or a black, dark-grey
or blackened material composition. Alternatively or additionally,
the element which is formed like a reflector can be provided, for
example coated, with black or dark-grey material or with a black or
dark-grey material composition. In particular, the element may be
manufactured completely or partially from plastic, with this
plastic being blackened for example by dyes, or soot-like or
soot-similar particles. In the visible spectral range, a material
or a material composition is regarded as being black if the
material is designed to be sufficiently greatly absorbent
consistently over this spectral range to be perceived as black. In
particular, a blackened material means a material which is
perceived as grey or dark grey.
[0025] According to a further preferred refinement, the
optoelectronic component comprises a housing body which preferably
contains the element which is formed like a reflector. Furthermore,
the optoelectronic component preferably comprises an external
connecting conductor on which the semiconductor chip is mounted
and, in particular, makes electrical contact. The semiconductor
chip is typically electrically conductively connected to a second
external connecting conductor.
[0026] In particular, the electrical connecting parts can be
surrounded by the housing body. The optoelectronic component may be
formed in the so-called premoulded housing form, in which the
housing body is prefabricated. The semiconductor chip in this
refinement can be mounted on an electrical connecting conductor
which is already surrounded by the housing body. The external
connecting conductors, which may be formed by means of a leadframe
allow external electrical contact to be made with the semiconductor
chip and may be electrically conductively connected to conductor
tracks on a connecting mount, for example a printed circuit board.
The electrical connection is preferably made by soldering, in
particular lead-free soldering.
[0027] In a preferred refinement, the optoelectronic component
comprises a thermal connecting part which is used to make thermal
contact with the optoelectronic component.
[0028] This thermal connecting part is preferably formed in
addition to the electrical connecting conductor. The heat which is
generated during operation of the optoelectronic component can
advantageously be dissipated, largely independently of the
electrical connections, by means of a thermally conductive
connection of this thermal connecting part to an external heat
sink.
[0029] In a further preferred refinement, the element which is
formed like a reflector is formed by means of a wall of a cavity in
the housing body. The semiconductor chip is particularly preferably
arranged in the cavity. An arrangement such as this allows the
semiconductor chip to be protected in a simpler manner against
external mechanical influences. Furthermore, the absorbent form of
the element which is formed like a reflector allows the majority of
the radiation which is output from the semiconductor chip and which
would strike the radiation outlet surface only as a consequence of
reflection, to be predominantly absorbed. Single and multiple
reflections of radiation within the lighting arrangement, with this
scattered radiation subsequently emerging from the lighting
arrangement at an angle which can be controlled only with
difficulty, are in this way advantageously reduced.
[0030] In a further preferred refinement, the housing body contains
a ceramic or a plastic, or is partially or completely manufactured
from a ceramic or a plastic. Ceramic is normally distinguished by
good thermal conductivity, so that the heat which is produced
during operation of the optoelectronic component can be dissipated
efficiently. Housing bodies based on plastics can be manufactured
at particularly low cost.
[0031] In a further preferred refinement, the housing body, in
particular the element which is formed like a reflector, is
manufactured completely or partially from a material which
specifically absorbs the radiation which is generated in the
optoelectronic component. Alternatively or additionally, the
housing body, in particular that wall of the cavity of the housing
body which forms the element which is formed like a reflector, can
be completely or partially black, blackened or suitably coated. For
example, soot-like or soot-similar particles or dyes can be used in
order to colour plastic black or dark grey.
[0032] In a further preferred refinement, the semiconductor chip is
embedded in a sheath, which in particular is transmissive to the
radiation which is generated in the semiconductor chip. This sheath
can cover the semiconductor chip, in particular completely. An
electrical contact for the semiconductor chip, for example a
bonding wire, can also be covered by the sheath. The sheath is
preferably designed to be sufficiently dimensionally stable to
allow it to protect the chip, and if appropriate the bonding wire,
against damaging external influences, for example mechanical
loading. For example, the sheath may contain a reaction resin, a
silicone resin or a silicone.
[0033] In a further preferred refinement, an intermediate layer is
formed between the sheath and the optical apparatus and is
particularly preferably directly adjacent to the optical apparatus
and to the sheath. The intermediate layer is preferably used as a
refractive-index matching layer between the sheath and the optical
apparatus.
[0034] In a preferred refinement, the optical apparatus has an
optical axis which preferably runs through the semiconductor chip,
in particular essentially through the centre of the semiconductor
chip, for example the centre of gravity of a laterally running
cross-sectional area of the semiconductor chip.
[0035] In a further preferred refinement, the optical apparatus has
a radiation inlet surface which faces the optoelectronic component.
The radiation inlet surface expediently faces that surface of the
semiconductor chip which is used to emit radiation. The minimum
distance between the semiconductor chip and the radiation inlet
surface is preferably 3 mm or less, particularly preferably 1 mm or
less, for example 0.6 mm.
[0036] The minimum distance between the radiation outlet surface of
the optical apparatus and the surface of the semiconductor chip is
preferably 5 mm or less, preferably 3 mm or less, for example 2 mm.
The reduction in the scattered radiation allows reliable
beamshaping by means of the optical apparatus with very short
distances between the optical apparatus and the semiconductor chip.
The lighting arrangement can therefore be manufactured to be
particularly compact.
[0037] In a preferred refinement, the radiation outlet surface is
rotationally symmetrical with respect to the optical axis. An
emission characteristic which is essentially rotationally
symmetrical with respect to the optical axis can be achieved in
this manner. Parts of the optical apparatus which are not used
mainly for beamshaping but, for example, are provided for mounting
the optical apparatus on the optoelectronic component, can be
designed such that they are not rotationally symmetrical with
respect to the optical axis.
[0038] In a preferred refinement, the radiation outlet surface of
the optical apparatus has a concave-curved subarea and a
convex-curved subarea which at least partially surrounds the
concave-curved subarea. The optical axis preferably passes through
the concave-curved subarea and particularly preferably at the same
time through the semiconductor chip, in particular essentially
through its centre, for example the centre of gravity of a
laterally running cross-sectional area of the semiconductor chip.
Radiation which is generated in the optoelectronic component and
directly strikes the concave-curved subarea in a manner which is
not coincident with the optical axis is predominantly deflected
away from the optical axis.
[0039] This reduces the proportion of the radiation which
propagates essentially in the direction of the optical axis, for
example at an angle of 20.degree. or less with respect to the
optical axis. In contrast, the radiation component which leaves the
lighting arrangement at large angles with respect to the optical
axis, for example 30.degree. or more, is increased. The radiation
power which is emitted from the lighting arrangement preferably
has, as a function of the angle with respect to the optical axis, a
maximum at comparatively large angles of 30.degree. or more, for
example at an angle between 60.degree. and 70.degree.,
inclusive.
[0040] A lighting arrangement having an emission characteristic
such as this is particularly suitable for illumination of a surface
which extends essentially at right angles to the optical axis of
the lighting arrangement, and in particular for back-lighting of
display apparatuses, for example LCDs (liquid crystal displays).
The area to be illuminated is typically considerably larger than
the area of the semiconductor chip. An emission characteristic with
a maximum of the emitted radiation power at a large angle with
respect to the optical axis, preferably at an angle of 60.degree.
or more, is advantageous since this allows areas of the surface
which is to be illuminated at a correspondingly long distance from
the optical axis to be illuminated even when the distances between
the surface and the lighting arrangement are short. For example,
the back-lighting unit of an LCD can thus advantageously be
manufactured to be particularly compact, with a shallow physical
depth.
[0041] The convex-curved subarea preferably has a first subregion
and a second subregion, with the curvature of the first subregion
being less than the curvature of the second subregion. In this
case, the second subregion may be arranged at a greater distance
from the optical axis than the first subregion. The curvature of
the convex-curved subarea, in particular the curvature of the
second subregion, preferably increases as the distance from the
concave-curved subarea increases. Curvature which increases
continuously with the distance is preferable, but not essential. An
increase in the curvature can result in the component of radiation
which emerges at a large angle with respect to the optical axis
advantageously being increased. Uniform illumination of subareas of
the area to be illuminated which are located at a comparatively
long distance from the optical axis is therefore assisted.
[0042] Radiation which emerges from the surface in the
semiconductor chip and strikes the radiation outlet surface
directly is deflected by the latter particularly efficiently at a
large angle of 30.degree. or more with respect to the optical axis.
In contrast, scattered radiation would be passed predominantly in
the direction of the optical axis and would in consequence lead to
stronger illumination of the area to be illuminated, in the area of
its intersection with the optical axis. The specifically absorbent
form of the element which is formed like a reflector allows for
this scattered radiation component to be reduced. An area to be
illuminated can thus be illuminated with little scattered
radiation, over a large area and particularly homogeneously. In
particular, it is advantageously possible to reduce the formation
of more strongly illuminated areas which extend like islands around
the intersection of the area with the optical axis.
[0043] Furthermore, radiation which strikes the radiation outlet
surface from outside the lighting arrangement and passes through
the optical apparatus can also cause a scattered radiation
component if this radiation is reflected in the component and
emerges again through the radiation outlet surface of the optical
apparatus. This component of the radiation which emerges again is
also referred to as phantom light and can reduce the contrast ratio
of the display apparatus when using the lighting arrangement for
back-lighting of display apparatuses, such as LCDs or LCD
televisions. By means of the specifically absorbent form of the
element which is formed like a reflector, and in particular of the
entire housing body, the phantom light influence can be largely
suppressed, and this can lead to an advantageous increase in the
contrast ratio of the display apparatus.
[0044] In a preferred refinement, the optical apparatus is attached
to the optoelectronic component. For this purpose, the optical
apparatus may, for example, be in the form of attachment optics, in
particular optics which are placed on, optics which are plugged on
or optics which are snapped on. Alternatively or additionally, the
optical apparatus can be adhesively bonded to the optoelectronic
component.
[0045] In this case, plug-on optics means an optical apparatus
which has an attachment element which can be plugged into a
suitable mounting apparatus for the optoelectronic component, for
example a recess in the housing body. In addition, the attachment
elements can be hot swaged to the optoelectronic component after
the optical apparatus has been fitted, as a result of which the
optical apparatus is attached particularly robustly and permanently
to the optoelectronic component.
[0046] In the case of snap-on optics, the optical apparatus has an
attachment element which latches into a suitable mounting apparatus
for the optoelectronic component.
[0047] Optics which are placed on can be attached to the
optoelectronic component without engagement and/or without any
latching connection. Specific elements are not required for
attachment to the optoelectronic component in the case of optics
which are placed on. In addition, the optics which are placed on
can be adhesively bonded to the optoelectronic component.
[0048] The lighting arrangement and in particular the
optoelectronic component preferably have no diffusers and/or
luminescence converters since both scattering of radiation
generated in the optoelectronic component on diffusers as well as
absorption of the radiation followed by re-emission by luminescence
converters would lead to the emission from the optoelectronic
component being increasingly nondirectional. Furthermore, the
sheath and if appropriate the intermediate layer are preferably
clear. This allows the radiation which is provided by the
optoelectronic component to be shaped by the optical apparatus in a
simplified manner, according to a predetermined emission
characteristic.
[0049] In a further preferred refinement, the optoelectronic
component is a surface mountable device (SMD).
[0050] The lighting arrangement is particularly preferably formed
with the optoelectronic component and the optical apparatus
attached to the optoelectronic component as a composite component.
As a composite component, the lighting arrangement can be fitted
more easily as an entity, for example on a printed circuit board.
The composite component is preferably in the form of a surface
mountable device.
[0051] Further features, advantageous refinements and expedient
features of the invention will become evident from the following
description of the exemplary embodiments, in conjunction with the
figures, in which:
[0052] FIG. 1 shows a schematic section view of a first exemplary
embodiment of a lighting arrangement according to the
invention,
[0053] FIG. 2 shows a schematic section view of a second exemplary
embodiment of a lighting arrangement according to the
invention,
[0054] FIG. 3 shows an example of a schematic illustration of the
beam profile of a lighting arrangement according to the
invention,
[0055] FIG. 4 shows a schematic section view of a semiconductor
chip which is particularly suitable for a lighting arrangement
according to the invention,
[0056] FIG. 5A shows a schematic perspective view of a lighting
arrangement according to the invention,
[0057] FIG. 5B shows a schematic section view through a lighting
arrangement as shown in FIG. 5A, in the form of a perspective
illustration,
[0058] FIG. 6A shows an example of the emission characteristic
(relative intensity I as a function of the angle .theta. with
respect to the optical axis) of a lighting arrangement having an
element which is formed like a reflector and is designed not to be
specifically absorbent,
[0059] FIG. 6B shows an example of the emission characteristic
(relative intensity I as a function of the angle .theta. with
respect to the optical axis) of a lighting arrangement according to
the invention with an element which is formed like a reflector and
is designed to be specifically absorbent,
[0060] FIG. 7A shows an example of the relative illumination
intensity B as a function of the distance d to the optical axis for
a lighting arrangement having an element which is formed like a
reflector and is designed not to be specifically absorbent,
[0061] FIG. 7B shows an example of the relative illumination
intensity B as a function of the distance d to the optical axis for
a lighting arrangement according to the invention having an element
which is formed like a reflector and is designed to be specifically
absorbent.
[0062] Identical elements, elements of the same type and elements
having the same effect are provided with the same reference symbols
in the figures.
[0063] FIGS. 1 and 2 show two exemplary embodiments of a lighting
arrangement 1 according to the invention. The lighting arrangement
in each case comprises an optical apparatus 4, an optoelectronic
component 2 and an element 3 which is formed like a reflector and
is designed to be specifically absorbent. Radiation which is
generated by the optoelectronic component 2 emerges from the
lighting arrangement through a radiation outlet surface 41 of the
optical apparatus.
[0064] Furthermore, the optoelectronic component contains a
semiconductor chip 5 which is provided for radiation production and
is preferably a thin-film semiconductor chip. A typical
configuration of a thin-film semiconductor chip will be described
in more detail in conjunction with FIG. 4.
[0065] The optoelectronic component 2 comprises the element 3 which
is formed like a reflector. The optoelectronic component 2 also
contains a housing body 20. The element 3 which is formed like a
reflector is formed by a wall 245 of a cavity 240 of the housing
body. The semiconductor chip 5 is arranged in the cavity 240 in the
housing body 20.
[0066] The housing body 20 may contain a ceramic or may be produced
completely or partially from a ceramic. Ceramic is typically
distinguished by high thermal conductivity, as a result of which
heat which is generated during operation of the optoelectronic
component can be dissipated efficiently via the housing body.
Alternatively, the housing body can be manufactured from plastic,
for example using an injection-moulding, transfer moulding or
pressure-casting process. Housing bodies composed of plastic can be
produced at particularly low cost. Furthermore, the same moulds can
be used as for the production of light-emitting diodes, in which
the housing bodies are made as highly reflective as possible in
order to maximise the radiation power which is emitted from the
light-emitting diode. There is advantageously no need for costly
moulds to be newly produced.
[0067] The element 3, which is formed like a reflector, is designed
to be specifically absorbent for the radiation which is generated
in the optoelectronic component. For this purpose, the element 3
which is formed like a reflector and, furthermore, the housing body
20 can be manufactured completely or partially from a material
which absorbs the radiation which is generated in the
optoelectronic component, or from an absorbent material
composition. The element which is formed like a reflector and in
particular the housing body are preferably black or dark grey. For
example, a housing body composed of plastic can be made black or
dark grey by the addition of dyes, or soot-like or soot-similar
particles to the plastic compound that is used.
[0068] Alternatively or additionally, the element 3 which is formed
like a reflector, and in particular the housing body 20, may be
provided, for example coated, for instance printed or stamped, with
a material which absorbs the radiation generated in the
optoelectronic component or with an absorbent material
composition.
[0069] In particular, the remaining reflectivity of the element 3
which is formed like a reflector and is designed to be specifically
absorbent is, in the wavelength range of the radiation which is
emitted by the optoelectronic component, 49% or less, preferably
30% or less, preferably 15% or less, particularly preferably 5% or
less.
[0070] Furthermore, the semiconductor chip 5 is mounted on a first
electrical connecting conductor 205, which preferably allows an
electrically conductive connection to an external connection, for
example a conductor track. A second electrical connecting conductor
206 may, for example, be electrically connected via a bonding wire
290 to the upper face 52, facing away from the electrical
connecting conductor, of the semiconductor chip. The ends 207 of
the first connecting conductor 205 and of the second connecting
conductor 206 can be attached to a printed circuit board 280 by
means of a solder 270, in particular a lead-free solder.
[0071] The first electrical connecting conductor 205 and the second
electrical connecting conductor 206 are surrounded by the housing
body 20 and project from different faces of the housing body. The
first and the second electrical connecting conductors are
preferably formed by a leadframe for the optoelectronic component
2.
[0072] Furthermore, the optoelectronic component 2 is embodied as a
surface mountable device. The lighting arrangement 1 can be formed
with the optoelectronic component 2 and the optical apparatus 4 as
a composite component.
[0073] In comparison to individual mounting of the optoelectronic
component and the optical apparatus, a lighting arrangement which
is in the form of a surface mountable composite device can be
mounted more easily on the printed circuit board 280.
[0074] The cavity 240 in the housing body contains a sheathing
compound 250, in which the semiconductor chip 5 and the bonding
wire are embedded. In this case, it is advantageous for them to be
embedded completely. This sheath is used to protect the
semiconductor chip 5 and the bonding wire against damaging external
influences and mechanical loads. The sheathing compound is
expediently designed to be transmissive to the radiation that is
generated by the semiconductor chip.
[0075] Furthermore, an intermediate layer 260 is introduced between
the sheathing compound 250 and a radiation inlet surface 46 of the
optical apparatus 4, which is particularly preferably directly
adjacent to the sheathing compound and to the radiation inlet
surface. This intermediate layer can be used for refractive-index
matching between the sheath and the optical apparatus.
[0076] The optoelectronic component, the intermediate layer and the
sheath are preferably assigned to be essentially free of diffusers
and/or luminescence converters. A more non-directional emission can
be avoided, as a result of which the radiation which is provided by
the optoelectronic component can be shaped by the optical apparatus
more easily, according to a predetermined emission
characteristic.
[0077] An optical axis 40 of the optical apparatus 4 runs through
the semiconductor chip 5, and particularly essentially through the
centre of the semiconductor chip. The optical axis is preferably at
right angles or essentially at right angles to the surface 52 of
the semiconductor chip 5. The optical apparatus comprises a
beamshaping part 48 and a mount part 49. The mount part is provided
for attaching the optical apparatus to the optoelectronic
component.
[0078] The beamshaping part 48 and the mount part 49 of the optical
apparatus 4 can be manufactured from different materials, and in
particular can be integrally formed on one another. If the
beamshaping part and the mount part are integrally formed on one
another, this makes it easier for the mount part to be mechanically
robustly connected to the beamshaping part without use of adhesion
promoters. The materials for the mount part and the beamshaping
part may be chosen for different requirements. In the case of the
beamshaping part, optical characteristics such as transparency and
radiation resistance for radiation emitted by the optoelectronic
component are particularly important.
[0079] The beamshaping part 48 preferably contains a silicone or
silicone hybrid material or is composed of a material such as this.
In contrast, the mount part 49 is not provided for beamshaping and
can therefore also be designed to be opaque to radiation. The
material for the mount part can be selected for particular
requirements such as mechanical robustness or good attachment
characteristics. A thermoplastic or a thermosetting plastic is
particularly suitable for manufacturing the mount part.
[0080] The distance between the radiation inlet surface 46 of the
optical apparatus and the surface of the semiconductor chip 52 is 5
mm or less, preferably 3 mm or less, preferably 1 mm or less, and
particularly preferably about 0.6 mm. The lighting arrangement can
therefore advantageously be manufactured in a particularly compact
form.
[0081] While, in the case of the exemplary embodiments shown in
FIGS. 1 and 2, the beamshaping part of the optical apparatus is
designed in the same way as that described in conjunction with FIG.
3, the two exemplary embodiments differ in the form of the mount
part and the type of attachment to the optoelectronic
component.
[0082] In FIG. 1, the optical apparatus 4 is in the form of plug-on
optics. In this case, the mount part 49 may have an attachment
element 49A like a pin, which can be plugged into a suitable
mounting apparatus of the optoelectronic component 2. The mounting
apparatus is preferably formed by a recess or a cut-out 201 in the
housing body 20. In addition, the attachment element can be
hot-swaged to the optoelectronic component after the optical
apparatus has been fitted, thus resulting in the optical apparatus
being attached to the optoelectronic component in a robust and
permanent manner.
[0083] FIG. 2 shows the optical apparatus as optics which are
placed on. A mount part 49 surrounds the housing body 20 laterally,
in particular completely. In this case, the mount part can clasp an
outermost side surface of the housing body. Furthermore, the mount
part may be laterally separated from the housing body over a large
area. In this case, complete separation is advantageous.
[0084] The intermediate layer 260 at least partially fills the
volume between the optical apparatus 4 and the housing body 20. The
volume between the sheathing compound 250 and the radiation inlet
surface 46 is preferably completely filled by the intermediate
layer. Furthermore, in the case of optics which are placed on, the
intermediate layer preferably clasps the housing body. The
intermediate layer may contain or be composed of a silicone, in
particular a silicone gel, or a silicone hybrid material. The
intermediate layer can therefore at the same time carry out the
function of a refractive-index matching layer and can be used for
simple, robust and permanent attachment of the optical apparatus 4
to the optoelectronic component 2.
[0085] The exemplary embodiments of a lighting arrangement shown in
FIGS. 1 and 2 are preferably provided for homogeneous illumination
of a surface 80 which runs essentially at right angles to the
optical axis 40. Since the area to be illuminated is typically
considerably larger than the surface of the semiconductor chip 5,
it is necessary for uniform illumination for as large a proportion
as possible of the radiation which is generated in the
optoelectronic component 2 to leave the radiation outlet surface 41
at a large angle with respect to the optical axis. The maximum of
the emitted radiation power as a function of the angle with respect
to the optical axis preferably occurs at an angle of greater than
or equal to 50.degree., particularly preferably greater than or
equal to 60.degree., for example about 70.degree.. A possible shape
for the beamshaping part 48 of the optical apparatus 4 of a
lighting arrangement 1 such as this, and the method of operation of
the optical apparatus 4, will be explained with reference to FIG.
3. The design of the illustrated lighting arrangement corresponds
in this case to that from FIGS. 1 and 2. For clarity reasons,
however, the figure does not show some of the details of the
lighting arrangement, which are not critical to the principle of
beamshaping by the optical apparatus 4, according to an emission
characteristic predetermined for the lighting arrangement, for the
radiation which is generated by the semiconductor chip 5 in an
active area 51.
[0086] The radiation inlet surface 46 is essentially flat. The
beamshaping of the radiation which is generated in the
optoelectronic component, according to an illumination intensity
distribution which is predetermined for the lighting arrangement,
preferably predominantly takes place on the radiation outlet
surface, thus allowing reliable beamshaping in a simplified
manner.
[0087] The radiation outlet surface 41 of the optical apparatus is
preferably rotationally symmetrical with respect to the optical
axis 40 of the optical apparatus 4. Parts of the optical apparatus
which are not used for beamshaping, for example the mount part 49
which is shown in FIGS. 1 and 2, may in this case be formed without
rotational symmetry.
[0088] Furthermore, the radiation outlet surface 41 has a
concave-curved subarea 42. The optical axis 40 of the optical
apparatus 4 runs through the concave-curved subarea.
[0089] The concave-curved subarea 42 is surrounded by a
convex-curved subarea 43, in particular completely. The area
content of the convex-curved subarea is preferably greater than the
area content of the concave-curved subarea. Furthermore, the
convex-curved subarea has a first convex-curved subregion 44 and a
second convex-curved subregion 45.
[0090] The radiation which is generated in the active area 51 of
the semiconductor chip 5 emerges through a surface 52 of the
semiconductor chip and a side surface 53. The effect of the optical
apparatus 4 on the radiation emerging from the surface is
illustrated by way of example on the basis of the beams 60, 61 and
62.
[0091] For radiation 60 which strikes the concave-curved subarea 42
of the radiation outlet surface 41, the optical apparatus acts like
a divergent lens. Radiation which strikes the concave-curved area
of the radiation outlet surface obliquely with respect to the
optical axis 40 or at a distance other than zero parallel to the
optical axis is therefore refracted away from the optical axis.
This advantageously reduces the radiation component which strikes
the surface 80 to be illuminated in the area close to the optical
axis. Radiation 61 and 62 which respectively strikes the first 44
and the second 45 convex-curved subregion is likewise refracted
away from the optical axis. The second convex-curved subregion 45
is preferably more sharply curved than the first convex-curved
subregion since radiation 62 which strikes the second subregion can
therefore be refracted particularly efficiently at a large angle
with respect to the optical axis.
[0092] The radiation outlet surface 41 is preferably formed without
any sharp transitions, that is to say the entire radiation outlet
surface is a surface which can be differentiated at any point, in
particular at a transition 47 between the concave-curved subarea 42
and the convex-curved subarea 43. Brighter or darker areas caused
by sharp transitions, for example rings of higher intensity on the
surface to be illuminated, can therefore advantageously be avoided.
Furthermore, the beam paths in or on the optical apparatus
preferably run essentially without any total internal
reflection.
[0093] The optical apparatus is preferably also designed such that
any two beams which originate from the region of the active area 51
through which the optical axis passes do not cross over after
emerging from the radiation outlet surface 41. Beams which cross
over may have the effect of local focusing of radiation in such a
way that this can result in inhomogeneities in the illumination
intensity, for example in the form of rings or circles of
relatively high intensity, being formed on the surface 80 to be
illuminated for the lighting arrangement. For the case of an ideal
point light source which is arranged on the optical axis, such
local focusing can thus be completely avoided.
[0094] In particular, radiation which is subject to reflection
before striking the radiation outlet surface 41 of the optical
apparatus 4 can cause beam paths that cross over. This is
illustrated by the beams 70 shown in FIG. 3, which emerge through
the side surfaces 53 of the semiconductor chip 5.
[0095] Arrows with dashed lines 71 and 72 for the beams 70 indicate
how the beams would run after reflection on the element which is
formed like a reflector if the element 3 which is formed like a
reflector were not designed to be specifically absorbent for
radiation generated in the semiconductor chip, as described in
conjunction with FIG. 1, but, for example, were to result in
directional reflection of incident radiation because of a metallic
coating, for example. For example, the beams 71 and the beams 70,
as well as the beams 72 and the beams 61, would cross after
emerging from the radiation outlet surface 41. This could result in
areas of increased illumination on the surface to be illuminated,
for specific distances between the surface 80 and the radiation
outlet surface. The specifically absorbent form of the element
which is formed like a reflector reduces the amount of radiation
striking the radiation outlet surface after previously having been
reflected on the element 3 which is formed like a reflector. The
radiation which strikes the optical apparatus is therefore
predominantly that which emerges from the semiconductor chip from a
precisely defined area of the surface 52 of the semiconductor chip
S. In this sense, the radiation which strikes the optical apparatus
approximates to the radiation which is emitted from an ideal point
light source. Crossing beam profiles can thus largely be avoided,
thus allowing particularly homogeneous illumination of the surface
80 to be illuminated.
[0096] Furthermore, in the case of directional reflection on the
element which is formed like a reflector, neither the beam 71 which
would be deflected on the concave-curved subarea 42 of the
radiation outlet surface 41 nor the beam 72 which would strike the
convex-curved subarea 43 are refracted away from the optical axis
but in fact predominantly lead to illumination of the subarea of
the surface 80 to be illuminated, close to the optical axis. This
central area of the surface would thus be more strongly
illuminated. An element which is formed like a reflector and is
designed to be diffusely reflective with a high reflection
coefficient, for example an element which is formed like a
reflector and is formed by a white plastic surface, would cause a
scattered light component to an increased extent and in consequence
stronger illumination of the surface to be illuminated in the area
close to the intersection with the optical axis, for example at a
distance of 10 mm or less from the optical axis. Because of the
specifically absorbent form of the element which is formed like a
reflector, a particularly homogeneous illumination of a surface to
be illuminated, for example a display apparatus such as an LCD, can
be achieved.
[0097] In the case of a lighting arrangement which is intended for
back-lighting of a display apparatus, the housing body is
preferably designed to be specifically absorbent in its entirety
for the entire visible spectral range. Inhomogeneous illumination
resulting from phantom radiation can thus be reduced to a
particularly major extent.
[0098] The major reduction in the scattered light component in
general simplifies the beamshaping of the radiation which is
generated in the optoelectronic component according to an emission
characteristic which is predetermined, in particular directionally,
for the lighting arrangement.
[0099] FIG. 4 shows a schematic sectional view of a exemplary
embodiment of a semiconductor chip 5 which is particularly suitable
for the optoelectronic component.
[0100] The semiconductor chip 5 comprises a semiconductor body 54
which is arranged on a carrier 55. The semiconductor body comprises
a semiconductor layer sequence with an active area 51 which is
provided for radiation production. The semiconductor layer sequence
forms the semiconductor body 54. A first contact 58 is arranged on
the side of the semiconductor body facing away from the carrier,
via which first contact 58 the semiconductor chip can be
electrically connected to a second contact 59, which is arranged on
the side of the, carrier facing away from the semiconductor body.
The first contact 58 is provided in particular for electrically
conductive connection to a bonding wire, and the second contact 59
is provided for electrically conductive connection to a connecting
conductor. By way of example, the contacts may each contain a metal
or an alloy.
[0101] In a preferred refinement, the semiconductor body 54, in
particular the active area 51, contains at least one III-V
semiconductor material, for example a material from the material
systems In.sub.x Ga.sub.y Al.sub.1-x-yP, In.sub.x Ga.sub.y
Al.sub.1-x-y N or In.sub.x Ga.sub.y Al.sub.1-x-y As, in each case
with 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and x+y.ltoreq.1, in
particular with x.noteq.0, y.noteq.0, x.noteq.1 and/or y.noteq.1.
The semiconductor layer sequence is preferably produced using a
deposition process, in particular an epitaxial deposition process,
for example by means of MBE or MOVPE on a growth substrate.
[0102] III-V semiconductor materials are particularly suitable for
radiation production in the ultraviolet (In.sub.x Ga.sub.y
Al.sub.1-x-y N) through the visible (In.sub.x Ga.sub.y Al.sub.1-x-y
N, in particular for blue to green radiation, or In.sub.x Ga.sub.y
Al.sub.1-x-y P, in particular for yellow to red radiation) into the
infrared (In.sub.x Ga.sub.y Al.sub.1-x-y As) spectral range.
Furthermore, III-V semiconductor materials, in particular from the
stated material systems, can advantageously be used to achieve high
internal quantum efficiencies for radiation production.
[0103] In a further preferred refinement, the active area 51
comprises a heterostructure, in particular a
double-heterostructure. Furthermore, the active zone may comprise a
single or a multiple quantum-well structure. Particularly high
internal quantum efficiencies can be achieved by means of
structures such as these, in particular a multiple quantum-well
structure or a double-heterostructure.
[0104] For the purposes of the application, the expression
quantum-well structure covers any structure in which charge
carriers experience or can experience quantization of their energy
states by confinement. In particular, the expression quantum-well
structure does not include any details about the dimensionality of
the quantization. It therefore covers, inter alia, quantum wells,
quantum wires and quantum dots, and any combination of these
structures.
[0105] In a further preferred refinement, a mirror layer 56 is
arranged on the semiconductor body. The mirror layer is
particularly preferably arranged between the semiconductor body 54
and the carrier 55. By way of example, the mirror layer may be in
the form of a mirror layer containing metal, in particular an
essentially metallic mirror layer. Radiation which is generated in
the active area can be reflected on the mirror layer, thus
preventing absorption in the structures, for example the carrier,
which follow the mirror layer as seen from the active area. The
efficiency of the semiconductor chip 5 can thus be increased. For
example, the mirror layer contains Au, Al, Ag, Pd, Rh, Pt or an
alloy with at least one of these materials. Al, Pd, Rh and Ag have
particularly high reflectivity in the ultraviolet and blue spectral
range, and Au has particularly high reflectivity in the yellow,
orange and red into the infrared spectral range, as well.
Furthermore, the reflection on the mirror layer increases the
proportion of the radiation which emerges from the side of the
semiconductor body opposite the mirror layer 56.
[0106] A connection layer 57, by means of which the semiconductor
body is mounted on the carrier at the side of the mirror layer, can
be arranged between the carrier 55 and the mirror layer 56. The
connection layer 307 may, for example, be in the form of a solder
layer.
[0107] The semiconductor chip shown in FIG. 4 is in the form of a
thin-film semiconductor chip. In contrast to a conventional
semiconductor chip, in the case of a thin-film semiconductor chip,
the carrier is different from a growth substrate on which the
semiconductor layer sequence of the semiconductor body is
deposited, for example by means of epitaxy. The growth substrate
can be removed or thinned in places or completely, mechanically
and/or chemically. The carrier is used to make the semiconductor
body mechanically robust.
[0108] In contrast to the growth substrate, the carrier
advantageously need not comply with the stringent requirements
relating to crystalline purity but can in fact be selected on the
basis of other criteria, such as mechanical robustness, and thermal
or electrical characteristics.
[0109] The carrier 55 preferably has a comparatively high thermal
conductivity. For example, the carrier contains Ge. A carrier
containing GaAs can also be used.
[0110] The active area 51 is preferably electrically conductively
connected to the second contact 59 via the electrically conductive
carrier, the electrically conductive connection layer and the
electrically conductive mirror layer as well as the semiconductor
layer sequence of the semiconductor body.
[0111] If the carrier contains a semiconductor material, then the
carrier is preferably suitably doped to increase the
conductivity.
[0112] By way of example, in order to produce a thin-film
semiconductor chip, the semiconductor layer sequence of the
semiconductor body 54 is first of all produced on the growth
substrate. The semiconductor layer sequence forms the semiconductor
body 54. The mirror layer 56 is then applied to the side of the
prefabricated semiconductor body facing away from the growth
substrate, for example by means of vapour deposition or sputtering.
On the mirror layer side, the assembly with the semiconductor layer
sequence and the growth substrate thereon is connected via the
connection layer 57 to the carrier 55, following which the growth
substrate is removed or detached, for example by means of etching
or laser cutting.
[0113] A thin-film semiconductor chip, for example a thin-film
light-emitting diode chip, can also be distinguished within the
scope of the present invention by the following characteristic
features: [0114] a mirror layer is applied or is formed, for
example integrated as a Bragg mirror in the semiconductor layer
sequence, on a first main surface of a semiconductor body facing a
carrier element, for example the carrier 55, which semiconductor
body comprises a semiconductor layer sequence with an active area,
in particular an epitaxial layer sequence, and the mirror layer
reflects back at least a portion of the radiation which is
generated in the semiconductor layer sequence back into it; [0115]
the semiconductor layer sequence has a thickness in the region of
20 .mu.m or less, in particular in the region of 10 .mu.m; and/or
[0116] the semiconductor layer sequence contains at least one
semiconductor layer with at least one surface which comprises a
inter-mixing structure which, in the ideal case, leads to an
approximately ergodic distribution of the light in the
semiconductor layer sequence, that is to say it has a scattering
behaviour which is as ergodically stochastic as possible.
[0117] A fundamental principle of a thin-film light-emitting diode
chip is described by way of example in I. Schnitzer et al., Appl.
Phys. Lett. 63 (16), 18 Oct. 1993, 2174-2176 the disclosure content
of which is hereby incorporated by reference.
[0118] Thin-film semiconductor chips are distinguished, in
particular with a mirror layer, by advantageously high efficiency.
Furthermore, a thin-film semiconductor chip may have a cosinusoidal
emission characteristic which corresponds essentially to that of a
Lambert radiator. A semiconductor chip in the form of a surface
radiator can be generated in a simplified manner by means of a
thin-film semiconductor chip, in particular with a mirror layer
containing metal or a metallic mirror layer.
[0119] The surface 52 of the semiconductor body facing away from
the mirror layer is in the form of a main radiation output surface
in the illustrated thin-film chip. A side surface 53 forms a
secondary radiation outlet surface. The radiation power which
emerges from the main radiation output surface is in this case
greater than the radiation power which emerges from the secondary
radiation outlet surface. In particular, the sum of the radiation
power which emerges from the secondary radiation outlet surfaces is
less than the radiation power which emerges through the main
radiation output surface.
[0120] In thin-film semiconductor chips, the radiation power which
emerges from the side secondary radiation outlet surfaces is
decreased in favour of increased radiation power output from the
main radiation output surface. Since the lighting arrangement 1 is
preferably essentially intended to provide only the radiation which
emerges from the surface 52 of the semiconductor chip, while
radiation which emerges at the side is predominantly absorbed as
described in conjunction with FIG. 3 by the element 3 which is
formed like a reflector and is designed to be specifically
absorbent, the radiation power emitted from the lighting
arrangement 1 is thus advantageously increased. Thin-film
semiconductor chips are therefore particularly suitable for use as
a radiation source.
[0121] It should be noted that the lighting arrangement can, of
course, be implemented not just by means of a thin-film
semiconductor chip. A semiconductor chip in which the growth
substrate is not detached may also be suitable for the lighting
arrangement. A semiconductor chip such as this may be configured as
shown in FIG. 4. In this case, the carrier 55 is formed by the
growth substrate. There is then no need for the connection layer
57. The mirror layer 56 can be dispensed with or it may be in the
form of a Bragg mirror, comprising a sequence of layers, for
example as part of the semiconductor layer sequence of the
semiconductor body 54.
[0122] A further exemplary embodiment of a lighting arrangement is
shown in FIGS. 5A and 5B, with FIG. 5A illustrating a perspective
view and FIG. 5B illustrating a perspective section view. As
described in conjunction with FIGS. 1 and 2, the lighting
arrangement 1 comprises an optoelectronic component 2 in which an
element which is formed like a reflector is formed by a wall 245 of
a cavity 240 of a housing body 20 and is designed to be
specifically absorbent for radiation which is generated in the
optoelectronic component. A thin-film semiconductor chip 5 is used
as the radiation source.
[0123] The cavity 240 is in the form of a recess in a first main
surface 202 of the housing body 20. A base 241 of the cavity
preferably runs essentially parallel to the first main surface. The
extent of the cavity on a plane which extends parallel to the first
main surface preferably decreases, in particular continuously, as
the distance from the first main surface increases, such that the
base of the cavity has a smaller diameter than the diameter of the
cavity on the plane of the first main surface. By way of example,
the cavity may essentially be in the form of a truncated cone,
whose diameter decreases as the distance from the first main
surface increases.
[0124] Optics which are separate from the optoelectronic component
can be attached to the optoelectronic component, for example by
being plugged on or adhesively bonded on. This is not shown, for
clarity reasons.
[0125] In contrast to the optoelectronic component shown in FIGS. 1
and 2, the optoelectronic component comprises a thermal connecting
part 215 on which the semiconductor chip 5 is arranged. The thermal
connecting part extends in the vertical direction preferably from
the cavity 240 to a second main surface 204 of the housing body 20.
The thermal connecting part simplifies thermal connection over a
large area, in particular with respect to the chip mounting surface
on the thermal connecting part, between the semiconductor chip 5 at
the side of the second main surface and an external heat conducting
apparatus, for example a heat sink, for example composed of Cu.
Heat which is created during operation of the semiconductor chip
can thus be efficiently dissipated from the optoelectronic
component, thus advantageously increasing the efficiency and
lengthening the life of the optoelectronic component, particularly
when operated as a high-power component. The optoelectronic
component may be designed to generate a high radiation power with
advantageously better heat dissipation at the same time, because of
the thermal connecting part. An optoelectronic component such as
this is particularly suitable for illumination of surfaces, for
example for back-lighting of a display apparatus, such as an
LCD.
[0126] The thermal connecting part 215 is, for example, inserted or
plugged into a lug of a first connecting conductor 205, or is
connected in some other way to the first connecting conductor, in
particular electrically conductively and/or mechanically, laterally
circumferentially. Furthermore, the first main surface 202 of the
housing body 20 comprises a recess 213 which is formed in the wall
245 of the cavity. This recess is provided for an electrically
conductive connection of a second electrical connecting conductor
206 to the semiconductor chip 5, for example by means of the
bonding wire 290. The second connecting conductor 206 is preferably
raised above the chip mounting plane of the semiconductor chip 5 on
the thermal connecting part 215. The thermal connecting part can
also project at the side of the second main surface 204 out of the
housing body or can end essentially on the same plane as the
housing body. By way of example, the thermal connecting part
contains a metal of high thermal conductivity, for example Cu or
Al, or an alloy, for example a CuW alloy. A leadframe with a
connecting part formed in this way and with a housing body is
described in WO02/084749, the disclosure content of which is hereby
incorporated by reference.
[0127] The optoelectronic component described in conjunction with
FIGS. 5A and 5B may also, of course, be used as an optoelectronic
component in the lighting arrangements shown in FIGS. 1 and 2.
[0128] FIGS. 6A and 6B show how the emission characteristic of a
light arrangement according to the invention is advantageously
modified in comparison to that of a lighting arrangement in which
an element which is formed like a reflector is not designed to be
specifically absorbent. The figure shows a first measurement (FIG.
6A) of the intensity I emitted in the visible spectral range, in
arbitrary units, as a function of the angle .theta. with respect to
the optical axis for a first lighting arrangement, and a second
measurement (FIG. 6B) of the emitted intensity I in arbitrary units
as a function of the angle .theta. with respect to the optical axis
for a second lighting arrangement.
[0129] The second lighting arrangement is designed as described in
conjunction with FIGS. 1 and 2. The first lighting arrangement is
physically identical to the second lighting arrangement, with the
element which is formed like a reflector not being designed to be
specifically absorbent, however.
[0130] The housing body 20 of the first lighting arrangement is
manufactured from high-reflectivity plastic, with reflectivities of
about 85% being achieved for the surface of the housing body, and
thus for the element which is formed like a reflector, by the
addition of TiO.sub.2 particles to the plastic compound. In
contrast, in the case of the second lighting arrangement, the
housing body and thus the element which is formed like a reflector
are designed to be specifically absorbent in that the plastic
compound from which the housing body is manufactured is coloured
black by the addition of soot-like particles, as a result of which
the reflectivity of the housing body in the visible spectral range
is about 5%.
[0131] A curve 400 shows the profile of the intensity of the
optical power emitted by the first lighting arrangement, as a
function of the angle with respect to the optical axis. In this
case, the intensity is normalized with respect to unity, and is
thus shown as a relative intensity.
[0132] In a corresponding manner, a curve 450 shows the emission
characteristic of the second lighting arrangement, with the
intensity curve once again having been normalized.
[0133] Both the curve 400 and the curve 450 have a global maximum
410 and 460, respectively, of the intensity at an angle of about
67.degree. to the optical axis. The described optical apparatus
accordingly results in the radiation which is generated in the
optoelectronic component not being emitted predominantly along the
optical axis.
[0134] Since the first and the second lighting arrangements differ
essentially only in the configuration of the element which is
formed like a reflector, the radiation which emerges through the
respective main radiation output surface 52 and strikes the
radiation outlet surface directly experiences essentially the same
beamshaping in both lighting arrangements. Differences between the
emission characteristic of the first and of the second lighting
arrangement therefore result predominantly from the radiation which
in each case leaves the semiconductor chip through a side surface
53.
[0135] In the first lighting arrangement, the element 3 which is
formed like a reflector is suitable, by virtue of its shape and
arrangement relative to the semiconductor chip which generates
radiation, for deflection onto the radiation outlet surface 41 of
at least a portion of the radiation which strikes the element which
is formed like a reflector. Because of the comparatively high
reflectivity of about 85%, a considerable proportion of the
radiation which emerges from the side surfaces 53 can therefore be
deflected onto the radiation outlet surface 41 of the optical
apparatus 4.
[0136] In the second lighting arrangement, the element which is
formed like a reflector is in contrast designed to be specifically
absorbent for the radiation which is generated in the semiconductor
chip, as a result of which the element which is formed like a
reflector deflects onto the radiation outlet surface only a
considerably smaller proportion of the radiation which emerges from
one of the side surfaces 53, because of the low reflectivity of
about 5%, despite its shape and arrangement.
[0137] In the region of large angles with respect to the optical
axis, for example between 45.degree. and 90.degree., the two curves
400 and 450 have a very similar profile. Radiation which is emitted
by the lighting arrangement in this angle range is predominantly
that radiation component which has been emitted from the main
radiation output surface of the respective semiconductor chip.
[0138] For smaller angles with respect to the optical axis, from
0.degree. to about 45.degree., the relative intensity 400 of the
radiation 420 which is emitted by the first lighting arrangement,
in particular in the angle range from 0.degree. to about
30.degree., is significantly higher than the relative intensity of
the radiation which is emitted by the second lighting arrangement
in the corresponding region 430. As described in conjunction with
FIG. 3, this is caused by scattered radiation which is deflected
onto the radiation outlet surface by the element which is formed
like a reflector, and emerges therefrom predominantly at angles
with respect to the optical axis 40 which are considerably less
than 60.degree., for example 40.degree. or less.
[0139] An emission characteristic with a maximum at angles of
60.degree. or more, with an additional reduction at the same time
in the radiation power emitted at small angles with respect to the
optical axis 40, can accordingly be achieved better by the
specifically absorbent version of the element which is formed like
a reflector.
[0140] The measurements of the illumination intensity distributions
shown in FIGS. 7A and 7B were carried out on the same components as
the measurements shown in FIGS. 6A and 6B. FIG. 7A and FIG. 7B
respectively show the illumination intensity distribution for the
first and the second lighting arrangement. Both the curve 500 for
the first lighting arrangement and the curve 550 for the second
lighting arrangement illustrate the illumination intensity B along
a straight line which runs at the side of the radiation outlet
surface 41 of the optical apparatus 4 at a distance of 25 mm over
the surface of the semiconductor chip 5 at right angles to the
optical axis 40. The distance d from the intersection of this
straight line with the optical axis is plotted using a millimetre
scale on the x-axis. The illumination intensity for both curves 500
and 550 is normalized with respect to the respective maximum value
which both curves assume at the intersection with the optical axis,
and is indicated on a relative scale, in undefined units.
[0141] Since the radiation outlet surface of the optical apparatus
is rotationally symmetrical with respect to the optical axis, and
the optical axis runs essentially through the centre of the
semiconductor chip, the two illumination intensity distributions
500 and 550 are essentially symmetrical with respect to the
y-axis.
[0142] In the region close to the y-axis, approximately for
|.parallel.|d|.ltoreq.10 mm, the profile 560 of the illumination
intensity for the second lighting arrangement differs considerably
from the profile 510 for the first lighting arrangement. While, in
the case of the curve 500, the illumination intensity when d=10 mm
has dropped by about 5% in comparison to the maximum value, the
corresponding drop of the second curve is only about 1%.
[0143] In the first lighting arrangement, radiation which emerges
from the side surfaces can be deflected onto the radiation outlet
surface 41 by the element which is formed like a reflector and has
high reflectivity. This radiation component strikes the radiation
outlet surface at an angle which can be controlled only with
difficulty, and can therefore be shaped by the optical apparatus 4
only with difficulty according to the emission characteristic
predetermined for the lighting arrangement. The deflection takes
place predominantly at comparatively small angles with respect to
the optical axis, thus leading to a peak in the illumination
intensity in the region 510. In contrast, in the second lighting
arrangement, the element which is formed like a reflector is
designed to be specifically absorbent, as a result of which
radiation which emerges from the side surface 53 of the
semiconductor chip is predominantly absorbed. The total radiation
power provided by the optical apparatus can thus be formed in an
improved manner according to a predetermined illumination intensity
distribution. As indicated by an arrow 561, this results in the
desired reduction in the illumination intensity in the region 560,
and in a slower drop in the illumination intensity as the distance
from the optical axis increases. For example, the drop in the
relative illumination intensity at d=30 mm is about 0.32 for the
curve 500, but only 0.22 for the curve 550.
[0144] A commonly used characteristic variable for the width of a
distribution is the full width at half maximum, which indicates how
broad the region around the maximum of the distribution is, in
which the function value of the distribution is 50% or more of the
maximum function value. This width is indicated by a horizontal
arrow 570 in FIG. 6b. The full width at half maximum of the curve
550 is in contrast advantageously broadened in comparison to that
of the curve 500 to about 84 mm in comparison to 76 mm for the
curve 500.
[0145] The measurements shown in FIG. 7 illustrate that the
illumination intensity distribution by means of an element which is
formed like a reflector and is designed to be specifically
absorbent can advantageously be significantly broadened. A surface
which is considerably larger than the surface 52 of the
semiconductor chip 5 can thus be illuminated particularly
homogeneously. The described second lighting arrangement is
therefore particularly suitable for back-lighting of display
apparatuses such as LCDs. As a result of the large-area
illumination with short distances between the surface to be
illuminated and the lighting arrangement, the physical depth of the
back-lighting unit can advantageously be kept small.
[0146] Furthermore, a lighting arrangement such as this can be
used, for example, for general lighting, effect lighting,
illumination of illuminated advertisement or for channel
letters.
[0147] The invention is not restricted by the description on the
basis of the exemplary embodiments. In fact, the invention covers
every new feature and every combination of features, in particular
including any combination of features in the patent claims, even if
this feature or this combination is not itself explicitly mentioned
in the patent claims or the exemplary embodiments.
* * * * *